Method of coating strip material



Nov. 30, 1965 H. R. JOHNSON 3,220,377

METHOD OF COATING STRIP MATERIAL Filed June 18, 1962 VACUUM 11 SOURCE\j'g. 5

Herschel R. Johnson INVENTOR.

United States Patent C) ice 3,220,877 METHOD OF COATING STRIP MATERIALHerschel R. Johnson, Rochester, N.Y., assignor to Eastman Kodak Company,Rochester, N.Y., a corporation of New Jersey Filed June 18, 1962, Ser.No. 283,036 9 Claims. (Cl. 117-120) This invention relates toimprovements in the method of applying liquid compositions or coatingmaterials to a moving strip of material to be coated.

It has been customary heretofore to utilize dip roll coating orapplicator roll coating, with or without a doctor blade to apply aliquid composition to a moving strip material or web so as to coat oneor both surfaces of the material. The liquid composition has also beenapplied to a moving strip material by pumping the composition through aslot in a hopper to coat the material. These methods have beensatisfactory in that uniform and usable coatings have been produced butthe speed of application is very limited. It is also very diflicult toattain a very thin coating by such methods. These disadvantages andlimitations are of a very serious nature in the photographic industrywhere many types of precise coatings on relatively nonporous supportsare required. In making color films which require multilayer coatings,the above methods have not only been time consuming but also difiicultto utilize because of the number of coatings required.

In US. Patent 2,681,294, a method of coating a moving 9 strip materialis disclosed which overcomes many of the disadvantages of the earliermethods as well as permitting the coating speed to be greatly increased.The method disclosed in this patent includes flowing a ribbon of theliquid composition in a stream between a coating device and a surface tobe coated while maintaining a greater pneumatic or other gaseouspressure on that side of the ribbon from which the coated material movesaway than on that side toward which the material to be coatedapproaches. Yet this method presents certain difficulties in starting acoating which results in a considerable loss of coated material. As themethod is practiced, the coating device in which the coating compositionis contained is usually positioned several inches from the material tostart the flow of the composition. The device is then moved toward thematerial and at the same time the suction is applied. The device ismoved almost into contact with the material and held in this positionuntil the coating bead is formed. Once the head has been properlyformed, the device is moved away from the material to a normal coatposition. Observation of the coated material at the start of coatingmade in this way indicates that there is an excessive laydown of thecomposition on the material at the instant of wetting and such excess ofthe liquid composition can extend for everal feet longitudinally of thematerial. This thicker layer does not dry as quickly as a layer ofnormal thickness and subsequently tracks oil onto the rollers forsupporting the material as it is moved through its drying or curingpath. The portion of the material coated with the thicker layer as wellas those portions of the material which have picked up streaks of thecoating composition from the support rolls cannot be used, and hence,must be cut out of the roll and scrapped. The thicker layer is formedwhenever the coating device is moved forward to start a new coatingoperation, and Whenever the coating device is moved out of its normalcoat position to restart the coating operation or to permit passage of asplice in the material.

In Observing the flow of the coating compositions and particularly theflow at the lip of the coating device or 3,220,877 Patented Nov. 30,1965 bead point, it was noted that an abnormally large welt or ridge ofthe coating composition forms at the lip, this welt or ridge apparentlybeing drawn up by surface tension forces and the nonwettable characterof the surfaces of the coating device. The disadvantages of the methoddescribed above have been overcome by utilizing a surge of higher thannormal suction as the coating device approaches the moving stripmaterial. This higher suction is maintained until the ribbon of coatingcomposition forms the necessary bead with the strip material and is thenreduced to the normal suction as the coating device is moved to its coatposition. As the lip of the coating device approaches the moving stripmaterial, a high velocity throat is formed with the strip material and acorresponding higher velocity of air flow through the throat resultstherefrom. The higher suction and the corresponding higher velocity ofair flow over the lip pulls the large welt or bead of coatingcomposition that has accumulated on the lip down over the lip andcarries it away in the air stream. The head that is formed as thecoating composition is then moved into contact with the moving stripmaterial immediately produces a uniform coating of the desiredthickness, the thicker layer normally prevalent at the start of acoating being completely eliminated with the removal of the accumulationof the coating composition at the lip of the coating device.

The primary object of the invention is, therefore, to provide a methodof applying a liquid composition to a moving strip material by which auniform layer of the liquid composition is immediately applied to thematerial.

A further object of the invention is to provide a method of applying aliquid composition to a moving strip material by which the coatingstarts are without any uncontrolled or abnormal layer of thecomposition.

Another object of the invention is to provide a method of applying aliquid composition to a moving strip material by which any accumulationof the composition on the lip of the coating device is removed beforethe composition is applied to the material.

And stil anothelr object of the invention is to provide a method ofapplying a liquid composition to a moving strip material by which anyaccumulation of the composition on the lip of the coating device isremoved by the air stream produced by different pressures on each sideof the lip of the coating device.

These and other objects and advantages will be ap parent to thoseskilled in the art by the description which follows.

Reference is now made to the accompanying drawing wherein like referencenumerals designate like parts and wherein:

FIG. 1 is a diagrammatic side elevation partially in section of a formof apparatus by which the improved method can be carried out;

FIG. 2 is an enlarged fragmentary sectional view showing theaccumulation of the liquid composition on the lip of the coating devicejust prior to removal thereof; and

FIG. 3 is an enlarged fragmentary sectional view showing the formationof the high velocity throat and the removal of the compositionaccumulation by the air stream moving through the throat just prior toformation of the coating bead.

With reference particularly to FIG. 1, the strip material ll), such asfilm or paper, is drawn from a supply source (not shown) and partiallywrapped around the roll or drum 11 for movement past the coating station12, the roll 11 being keyed or fixed to shaft 13 which is continuouslyrotated at a desired rate (feet per minute) in accordance with theliquid composition to be applied to the strip material. Thus, as theuncoated material 10 is moved into the coating station, the liquidcomposition 14 is applied thereto and then passes away from the roll 11for the necessary drying operations.

The coating device 15 can be of a type disclosed in US. Patents2,761,419 and 3,005,440 in which a fluid composition 16 is continuouslypumped by a constant discharge pump 17 into a cavity 18 at a given rate,the composition being forced through a narrow distributing slot 19 inthe form of a ribbon and onto a downwardly inclined slide surface 20.The ribbon flows by gravity in the form of a layer 21 .to the pointwhere it forms a coating bead 22 between the lip 23 of surface and themoving strip material 10. A second fluid composition 25 is pumped intocavity 26 by another constant discharge pump 27 and is forced throughthe distributing slot 28 in the form of a ribbon and onto the inclinedslide surface 29. As the layer 30 reaches the layer 21, it flowsthereover and the two layers then flow down surface 20 and into thecoating bead 22.

The coating device 15 extends axially with respect to roll 11 and ismounted on plate 32 which, in turn, is pivotally mounted on cross shaft33. By means of wheel 34 and lead screw 35, which is pivotally connectedto extension 36 on plate 32, the coating device can be moved toward andaway from material 10 and roll 11.

A casing 40 having end walls 41 together with coating device 15 and aportion of roll 11 form a chamber 42. A vacuum source or pump 43 isconnected to chamber 42 by pipe 44 which is provided with a regulatingvalve 45. The pressure within chamber 42 can be indicated by means, ofthe manometer 46 which is connected to chamber 42 by means of line 47.

When starting a coating operation, the coating device 15 is moved ortilted to a Start Coat position in which the lip 23 is separated byseveral inches from the material 10 and roll 11. In this position thefluid compositions must be pumped into the cavities 18 and 26 in orderthat the layers 21 and 30 of the compositions can be formed for flowingtoward the lip 23 of the coating device. In accordance with the methodtaught by US. Patent 2,681,294, the pressure within chamber 42 isreduced so that it is subatmospheric with a pressure differential of theorder of 0.1 inch to 5.00 inches of water depending on the fluidcomposition and the material to be coated. Since it is desirable to havelayers 21 and 30 at the lip 23 when the coating device is positionedrelative to material 10 to form bead 22, the coating device is not movedtoward the material 10 until the layers 21 and 30 are at the lip. Duringthe interval that the coating device 15 is moved toward material 10, awelt 50 of the fluid compositions accumulates at lip 23, as shown inFIG. 2. Although the air pressure on the side of the fluid compositionstoward which the material 10 approaches is subatmospheric and on theopposite side of the fluid compositions is atmospheric, the differentialin pressures is not great enough to create an air flow in the throatformed by lip 23 and material 10 as the layers approach material 10which is sufficient to remove the welt 50 from the lip..

In the present invention, the coating device 15 is in the Start Coatposition, as described above, for forming the layers 21 and 30. At thistime, the pressure differential between chamber 42 and the atmosphere isequivalent to that for the normal coating operation. However, as thecoating device 15 is moved toward material 10 and roll 11, valve isturned to increase the vacuum so as to increase the pressuredifferential. The initial pressure differential as well as the increasedpressure differential will vary in accordance with the fluidcompositions, the material to be coated and the rate at which thematerial is moved. The air pressure differential must, however, be greatenough to provide an air flow between lip 23 and material 10, as thecoating device 15 approaches material 10, so that the welt will beremoved from lip 23, as shown in FIG. 3, and carried by the air streaminto chamber 42. The increased air pressure differential is maintaineduntil coating device 15 has been moved sufliciently close to material 10so as to form bead 22 with layers 21 and 30 and the moving stripmaterial 10. After the bead 22 has been formed transversely of material10 and layers 21 and 30 are being applied uniformly to material 10, thecoating device is then moved away from material 10 into the Coatposition. At this time, the valve 45 is readjusted so the air pressuredifferential is reduced to that normally used for the coating operation.The position of lip 23 relative to the moving strip material for formingthe bead 22 and for maintaining a uniform coating application will alsobe dependent on the fluid composition, the material to be coated and therate of movement of the material.

In order to more clearly illustrate the applicability of the inventionwith respect to particular coating applications, several specificexamples are described hereinafter. It is to be understood, of course,that the invention is not to be limited to the materials nor the variousfactors set forth in these examples.

Example 1.--C0atir1g a single layer color filter This was a dispersionin aqueous solution which was applied to a dry subbed safety supportfrom a coating device such as shown in FIG. 1. The speed of coating was120 feet per minute. The air pressure differential used for coating wasequal to approximately 0.35 inch of water. The total amount of solutioncoated was 0.012 pound per square foot. The viscosity was approximatelyfour centipoise at F. The increased air pressure differential introducedduring the start of coating and beadmaking was 1.5 inches of water whichwas maintained for a brief period of time until the coating device wasmoved to Coat position. The air pressure differential was then reducedto 0.35 inch of water and held.

Example 2 .-C0at1'ng an anti-halatz'on layer A water solution of gelatincontaining a spreading agent, such as saponin, and a suitable dye wascoated as an anti-halation layer on the back of a safety support at 90feet per minute. The viscosity of the solution was approximately 10centipoise at F. This solution was applied from a coating device such asshown in FIG. 1. The total amount of solution applied was 0.0235 poundper square foot of support. The air pressure differential at the coatingbead was 0.5 of water. The increased air pressure differentialintroduced just before and during the start of coating and bead-makingwas 1.5 inches of water which was maintained for a brief period of timeuntil the coating device was moved to Coat position. The air pressuredifferential was then dropped back to 0.5 inch of water.

In addition to the above examples, reference can also be made to theexamples set forth in US. Patent 2,681,294 wherein various initial airpressure differentials are disclosed for coating other materials withdifferent fluid compositions. The increased air pressure differential tobe used in these examples will again be dependent on the material,composition and rate of movement of the material. While the improvedmethod of coating a moving strip material described herein can beutilized for many other applications, the invention is not to be limitedto the disclosed examples but is of a scope as defined by the appendedclaims.

I claim:

1. A method of applying a liquid composition to a relatively movingstrip material carried by a support which comprises:

forming a flowing stream of said liquid composition;

subjecting the flowing stream of liquid composition to an initialdifferential air pressure, the lesser air pressure being on the side ofthe flowing stream toward which the moving strip material approaches;increasing the initial differential air pressure as the flowing streamof liquid composition approaches the U moving strip material to removeany accumulation of the liquid composition at the end of the streamprior to engagement of the stream with the moving strip material;maintaining the increased differential air pressure until a bead ofliquid composition has been formed transversely of an area of the movingstrip material; and

decreasing the differential air pressure to the initial differential airpressure after the head has been formed.

2. A method of applying a liquid composition to a relatively movingstrip material carried by a support which comprises:

forming a flowing stream of the liquid composition;

subjecting the flowing stream of liquid composition to and initialdifferential air pressure, the pressure on the side of the flowingstream toward which the moving strip material approaches beingsubatmospheric and the pressure on the opposite side being atmospheric;

increasing the initial differential air pressure as the flowing streamof liquid composition approaches the moving strip material to remove anyaccumulation of the liquid composition at the end of the stream prior toengagement of the stream with the moving strip material;

maintaining the increased differential air pressure until a bead ofliquid composition has been formed transversely of an area of the movingstrip material; and decreasing the differential air pressure to theinitial differential air pressure after the bead has been formed. 3. Amethod of applying a liquid composition to a relatively moving stripmaterial carried by a support which comprises:

forming a flowing stream of the liquid composition; subjecting theflowing stream of liquid composition to a greater air pressure on thatside from which the coated strip leaves the flowing stream and to alesser air pressure on the other side, the air pressure differentialbeing of the order of .1" to 5.00" of Water;

increasing the initial differential air pressure as the flowing streamof liquid composition approaches the moving strip material to remove anyaccumulation of the liquid composition at the end of the stream prior toengagement of the stream with the material;

maintaining the increased differential air pressure until a bead ofliquid composition has been formed transversely of an area of the movingstrip material; and

decreasing the differential air pressure to the initial differential airpressure after the head has been formed. 4. A method of applying aliquid composition to a relatively moving strip material carried by asupport which comprises:

forming a flowing stream of said liquid composition; subjecting theflowing stream of liquid composition to an initial differential airpressure, the lesser air pressure being on the side of the flowingstream toward which the moving strip material approaches;

decreasing the lesser air pressure to obtain a differential air pressure2 to 15 times that of the initial differential air pressure as theflowing stream of liquid composition approaches the moving stripmaterial to remove any accumulation of the liquid composition prior toengagement of the stream with the material;

maintaining the increased differential air pressure until a bead ofliquid composition has been formed transversely of an area of the movingstrip material; and

decreasing the increased differential air pressure to the initialdifferential air pressure after the bead has been formed.

5. A method of applying a liquid composition to a relatively movingstrip material carried by a support which comprises:

forming a flowing stream of the liquid composition;

subjecting the flowing stream of liquid composition to a greater airpressure on that side from which the coated strip leaves the flowingstream and to a lesser air pressure on the other side, the air pressuredifferential being of the order of .1" to 5.00" of water;

decreasing the lesser air pressure to obtain a differential air pressure2 to 15 times that of the initial differential air pressure as theflowing stream of liquid composition approaches the moving stripmaterial to remove any accumulation of the liquid composition prior toengagement of the stream with the material; maintaining the increaseddifferential air pressure until a bead of liquid composition has beenformed transversely of an area of the moving strip material; and

decreasing the increased differential air pressure to the initialdifferential air pressure after the bead has been formed.

6. A method of applying a liquid composition contained in a coatingdevice to a relatively moving strip material carried by a support whichcomprises:

moving the coating device toward said moving strip material; subjectingthat side of the lip of the coating device toward which the strip ofmaterial approaches to an initial subatmospheric pressure whilemaintaining atmospheric pressure on the opposite side thereof;

decreasing the initial subatmospheric pressure so as to obtain a greaterpressure differential with respect to the atmospheric pressure as saidcoating device approaches the moving strip material for removing anyaccumulated liquid composition from the lip of the coating device;

maintaining the greater pressure differential until a bead of saidliquid composition has been formed transversely of an area of the movingstrip material; moving said coating device away from the moving stripmaterial after a formation of the bead to a position for providing auniform coating of the liquid composition on the moving strip material;and increasing the subatmospheric pressure to the initial subatmosphericpressure and maintaining the initial subatmospheric pressure while theliquid composition is being applied to the moving strip material.

7. A method of applying a liquid composition contained in a coatingdevice to a relatively moving strip material carried by a support whichcomprises:

flowing a thin layer of said liquid composition to the lip of thecoating device;

moving the coating device toward the moving strip material;

subjecting the flowing layer of liquid composition at the lip of thecoating device to an initial differential air pressure, the lesser airpressure being on the side of the flowing layer toward which the movingstrip material approaches;

increasing the initial differential air pressure as the flowing layerapproaches the moving strip material to remove any accumulation of theliquid composition on the lip of the coating device; maintaining theincreased differential air pressure as a bead of liquid composition isbeing formed transversely of an area of the moving strip material;

moving the coating device away from the moving strip material afterformation of the bead to a position for for applying a uniform coatingof the liquid composition to the moving strip material; and

decreasing the differential air pressure to the initial differential airpressure after the coating device has been moved into the applyingposition and maintaining the initial differential air pressure while theliquid composition is being applied to the moving strip material.

8,220,877 71 8 8. A method of applying a liquid composition contained ina coating device to a relatively moving strip tained in a coating deviceto a relatively moving strip l Carried by a Support which comprisesmaterial arried by a support hi h comprises; flowing a thin layer ofsaid hquid composition to the flowing a thin layer of said liquidcomposition to the lip of the coating device;

lip f the Coating device; moving the coating device toward the movingstrip t n ma eria 232; coating device toward the movmg Stnp subjectingthe layer of the liquid composition at the subjecting the layer of saidliquid composition at the hp of.the coatmg Slevlce to a greateiall-Pressure on lip of the coating device to an initial differential airthat.s1de from whlch the coaied strip W111 leave pressure, the pressureon the side of the layer to- -g lay-er and to a -i g on the otder wardwhich the moving strip material approaches be- $1 'E alr Bressure eremlamug of the or er of .1 to 5.00 of water, silbasmosphenc the Pressure theOPPO decreasing the lesser air pressure to obtain a differenslte 0f h P=5 tial air pressure 2 to times that of the initial difincreasing the1n1t1al differential air pressure as the 15 f ti l air pressure as thefl i layer f liquid coating device approaches the moving Strip materialcomposition approaches the moving strip material material to remove anyaccumulation of the liquid to remove any accumulation of the liquidcomposicomposition on the lip of the coating device; tion or the lip ofthe coating device; maintaining the increased ditferential air pressureas a maintaining the increased differential air pressure as head ofliquid composition is being formed transa bead of liquid composition isbeing formed transversely of an area of the moving strip material;versely of an area of the moving strip material; moving the coatingdevice away from the moving strip moving the coating devhfe y from themoving h p material after formation of the bead to a position material'f forlhatlon of F bead Positlon for applying a uniform coating of theliquid com- }PP a P cqfltmg the hquld position to the moving stripmaterial; and I posit on to the moving str p material; and I increasingthe subatmospheric pressure to the initial mcreasmg the ubatmosphencpressure 9 the 1 subatrnospheric pressure after the coating device isfigig gig g gfiiig gP223 g s g igi i ggg ig gg moved into the applyingposition and maintaining the initial subatmospheric pressure while theliquid comlnitial subatmospheric pressure while the liquid compositionis being applied to the moving Strip materiaL position is being appliedto the moving strip material. 9. A method of applying a liquidcomposition con- No references cited.

RICHARD D. NEVIUS, Primary Examiner.

1. A METHOD OF APPLYING A LIQUID COMPOSITION TO A RELATIVELY MOVINGSTRIP MATERIAL CARRIED BY A SUPPORT WHICH COMPRISES: FORMING A FLOWINGSTREAM OF SAID LIQUID COMPOSITION; SUBJECTING THE FLOWING STREAM OFLIQUID COMPOSITION TO AN INITIAL DIFFERENTIAL AIR PRESSURE, THE LESSERAIR PRESSURE BEING ON THE SIDE OF THE FLOWING STREAM TOWARD WHICH THEMOVING STRIP MATERIAL APPROACHES; INCREASING THE INITIAL DIFFERENTIALAIR PRESSURE AS THE FLOWING STREAM OF LIQUID COMPOSITION APPROACHES THEMOVING STRIP MATERIAL TO REMOVE ANY ACCUMULATION OF THE LIQUIDCOMPOSITION AT THE END OF THE STREAM PRIOR TO ENGAGEMENT OF THE STREAMWITH THE MOVING STRIP MATERIAL; MAINTAINING THE INCREASED DIFFERENTIALAIR PRESSURE UNTIL A BEAD OF LIQUID COMPOSITION HAS BEEN FORMEDTRANSVERSELY OF AN AREA OF THE MOVING STRIP MATERIAL; AND DECREASING THEDIFFERENTIAL AIR PRESSURE TO THE INITIAL DIFFERENTIAL AIR PRESSURE AFTERTHE BEAD HAS BEEN FORMED.